Electrical lighting systems are very inefficient and can contribute significantly to air conditioning loads, thereby increasing overall electricity costs. For instance, incandescent lights waste about 97% of their electrical energy as heat, and fluorescent lights waste about 90%.
In contrast, the sun is a high intensity energy source of freely available sunlight. In order to take advantage of this energy source, sunlight collectors can be made that are small and light enough to be mounted on conventional roofs, walls, window sills and the like, without the need for flashing or any significant structural alterations.
Attempts have been made to design such sunlight collectors. U.S. Pat. No. 4,539,625 describes a lighting system for a building interior that utilizes a solar light receiving stack of luminescent concentrators connected to an optical conduit consisting of optical fibers that transmit light to a fixture located in the area to be illuminated. However, the stack and optical conduit are very wide and this poses physical difficulties in installing the system since the stack located on the outside of the building will need to communicate with the optical conduit located in the interior by passing through a similarly wide aperture in the building wall or like barrier between inside and outside.
Additionally, a very wide optical conduit will have limited flexibility and accessability and so may not be able to access locations remote from the solar light receiving stack.
On the other hand, a relatively narrow, thin and flexible optical conduit would forseeably pose fewer, if any, problems in installation and accessibility to remote locations.
The solar light receiving stack or collector of U.S. Pat. No. 4,539,625, because of its relatively large width to length ratio, will only have an appreciable contribution from total internal reflection at the top surface, the bottom surface and the end opposite the optical conduit. There is no appreciable contribution from total internal reflection at the collector side edges. It is therefore reliant upon having a correspondingly wide optical conduit.
Furthermore, it is reliably anticipated that due to design flaws, the output colour of light from the system of U.S. Pat. No. 4,539,625 will not be neutral or near neutral.
It is therefore an object of the present invention to provide an improved means for lighting the interior of a building or the like which involves collecting sunlight and transmitting it to the interior of the building or the like.